Evidence that peer rejection is associated with significant child and adolescent maladjustment emphasizes the importance of early identification and intervention for young children at-risk for peer rejection. The proposed study will address gaps in the peer rejection literature by examining the stability of subgroups of children, the effects of different reporters (i.e. teacher, parent, and observations), and early antecedents of rejection in subgroups of children. Participants will be selected from a larger longitudinal study examining parent reports of infant-toddler social-emotional and behavior problems and social-emotional competence and later social-emotional and academic adjustment in kindergarten and second grade. The proposed study will focus on two groups of children: (1) all children in the birth cohort with parent and teacher survey data (expected N=719) and (2) approximately 150 children randomly sampled across aggressive/rejected subgroups for whom observational data will be collected. Data will be collected through questionnaires filled out by parents and teachers and observations of children in their second grade classroom. The information derived from this study will be useful in identifying children at-risk for peer rejection and the development of prevention and intervention efforts.